Venture Blog seems to agree with this post that claims no software company can succeed without a programmer at the helm. I would say that overall this rule is true. There are exceptions, like Gerstner at IBM, but more often than not, tech companies need someone who has some technical background.
I worked at Lexmark during a CEO change. CEO #1 had an economics degree and CEO #2 has a PhD in Electrical Engineering. Both did well, but I think Curlander (CEO #2) has done a better job. When I left, Curlander was tranforming Lexmark from a company focused on printers to one focused on the digital office. People often used to discuss the differences in the two CEOs, and I don't know how the marketing dept. felt, but the engineers were very happy with Curlander.
But, I think tech CEOs can sometimes cause problems too. Good business skills are necessary to run a company in any industry, and tech CEOs sometimes think good technology will make a good company. That's not true. You can have the coolest technology in the world, and if you can't market it properly, or if consumers aren't ready for it, you won't make any money. I guess that is why good CEOs are hard to find. People who understand tech and business and can apply what they know are rare.